An oil well cementing expert told a federal judge Thursday that BP should not have proceeded with the cement job the day before the ill-fated Macondo well blew out, despite knowing the hazards involved.

"Based on the culmination of all of the risks, again, I'll repeat, I don't see how you could pump this job in the well and expect it to form a barrier," Glen Benge, an independent consultant on oil-field cementing who was called as an expert witness by the Department of Justice, testified in the eighth day of the civil trial, which will determine liability for the massive 2010 oil spill.

Benge's testified for the second day Thursday. He said his review showed at least nine errors committed during the cementing of BP's Macondo well, which, when combined, led to the disaster, which killed 11 workers and triggered the 87-day uncontrolled release of oil and gas from the well into the Gulf of Mexico.

Benge said Wednesday that the cement pumped into the BP Macondo well a day before it blew out on April 20, 2010, was not allowed time to harden before a negative pressure test was run. That lapse allowed oil and natural gas to travel up the drill pipe to the surface, where it exploded aboard the Deepwater Horizon drilling rig.

Benge has laid much of the blame for the errors on BP, whose workers designed the cementing job and oversaw the work, and on Halliburton, which was hired by BP to provide the material.

Benge, who said he has participated in more than 1,000 well cementing jobs, and designed and oversaw the first use of foam cement in a well in Mobile Bay in 1995, concluded in a 2011 expert report that the cement didn't cut off the flow of hydrocarbons into the well.

In his nine years as a senior technical adviser for cementing at ExxonMobil, Benge testified that he relied on the company's cement contractor to "communicate any potential issues with the slurry design."

"It's on the contractor to report to the operator on how the job went, how we did, and how it was executed, correct?" BP attorney Matt Regan asked during cross-examination.

"That is correct," Benge replied.

Benge also testified that he saw no evidence BP used cement left over from an earlier drilling operation in order to trim costs; that Halliburton advised BP against using the extra cement, or that BP would have refused to pay for new cement if it was recommended.

In his 2011 expert report, Benge concluded the design of the slurry was inadequate, that it failed to perform as expected and that the cement was improperly placed in the well.

Investigators with the national Oil Spill Commission, the seven-member panel appointed by President Barack Obama in 2010, found that Halliburton used unstable cement to seal the well, and that the mixture had failed multiple tests in the weeks leading up to the disaster.

Commission investigators also learned Halliburton was aware of the issues but decided to proceed with using the cement mixture, Benge testified.

Benge also testified that BP's decision to use only six centralizers, rather than the 21 recommended by Halliburton engineers, meant sections of the drill pipe likely leaned closer to one side of the drillhole. When cement was pumped in to fill the space around the pipe, it could not fill in the narrow side, leaving a channel filled by drilling mud that hydrocarbons could use to reach the surface.

Halliburton had relied on a computer model April 15 that showed an adequate seal on the walls could be achieved as long as BP used 21 of the devices to help the cement set and keep the long central tube centered in the hole.

Jesse Gagliano, a Halliburton technical adviser who worked in the same office in Houston with the BP engineers, warned his clients that day of the chance that if the tube wasn't centered, cement poured in the hole could go toward the wider side, leaving a weaker barrier on the opposite side.

Benge testified Thursday that BP should have disclosed to Halliburton that it only planned to use six centralizers. At this point, Benge testified that BP attorneys were "going back after the fact and trying to determine ways that this cement job may have worked."

Had Halliburton received the information from BP, it could have updated its models to assess the risks of proceeding with the cement job, Benge testified.

"The operator and the service company, having been on both sides, they work together to achieve a successful cement job. You can't do it in isolation," Benge testified.

"Does that mean to you that BP absolved itself of responsibility for the cement job by relying on Halliburton's services?" Scott Cernich, an attorney for the Justice Department, asked Benge during redirect examination.

"No sir, it did not," Benge testified.

BP also did not test the mud at the bottom of the well before placing the final cement lining, according to testimony from the 2010 joint hearings by the US Coast Guard and the Bureau of Ocean Energy Management, Regulation and Enforcement, held to investigate the causes of the Deepwater Horizon disaster.

BP's top drilling supervisor on the rig, Jimmy Harrell, testified in 2010 that BP decided against conducting a "bottoms-up" test to examine the condition of the drilling mud, an area where a casing shoe was about to be placed. The casing shoe protects the well from natural gas or oil pressing in.

Benge's expert report, submitted on behalf of the Justice Department, states industry best practices call for conducting a bottoms-up test before pouring the cement. Circulating mud through the well hole could determine if natural gas has infiltrated the well, Benge testified.

Regan, hoping to discredit the significance of the test, pressed Benge under cross-examination about "how much cleaner
the bottom of the well would have been" it had been done.

"I'm not trying to be indelicate, but this is kind of like asking, 'How bad can it be and still be OK,' because bottoms-up circulation is a core for cementing," Benge testified.

Benge contended that the practice wasn't simply to tidy the bottom of the well. "That's just one thing," he testified. "I don't know if the mud that was left at the bottom of the well for several days had gas in it, what the condition of it was, the gels, that's why you do a bottoms-up circulation is to evaluate all of that."

Halliburton has acknowledged that it used the cement mixture under orders from BP, but did not test its stability before pouring it into the well. The cement mixture contained small nitrogen bubbles, which, combined with extreme heat and pressure, allowed it to expand and contrast in the drilled-out hole.